For many years Professor Eric Parmentier – who directs the Functional and Evolutionary Morphology Laboratory of the University of Liege - has been tracking sounds emitted by fishes in order to better understand the way they live. A recent study, unique in the world, has made it possible to compare the huge amount of sounds emitted by different fish communities at a depth of 120 meters. This research has been the subject of a publication in the prestigious American magazine PNAS (Proceedings of the National Academy of Sciences).

The sound environment of fishes and the way it is distributed have rarely been studied. Although we know today that fishes emit sounds, few studies have focused on how fishes are able to avoid cacophony. With the help of a hydrophone that the team was able to place at a depth of 120 meters, Professor Eric Parmentier recorded almost 2793 sounds which were analyzed by his team. This painstaking work aimed to characterize the sounds to better understand how the different species share the sound environment.

It was during the course of a meeting with a scientist from the Natural History Museum in Paris that Professor proposed to join a scientific mission directed by Laurent Ballesta, a former scientific collaborator with Nicolas Hulot. Laurent Ballesta (Andromeda-Oceanology), while in charge of a scientific documentary on the Coelacanth (a marine species that can be traced back to 350 million years ago!) -  accepted an offer by Eric Parmentier to take advantage of this field study in order to have a hydrophone installed in the observation area. It should be pointed out that the Cœlacanth only lives in two precise places in the world, one of which is Sodwana Bay in the South-Eastern coasts of South Africa. It was here that the team decided to proceed with its observations. So it was here at a depth of 120 meters (the Cœlacanth lives at depths between 100 and 800 meters) that the device prepared by Laurent Ballista’s team and Eric Parmentier’s hydrophone were placed at the entrance to a small cave.

For fifteen days the microphone recorded thousands of sounds, among which  2793 were kept for further analysis. These were divided into 17 main groups. These sounds were then painstakingly analyzed to demonstrate two broad communities: some species emit sounds by day and others by night. “While during the day, some frequencies of the different sounds tend to overlap, the sounds emitted at night showed more differences,  the fish have clearly developed a behavior relative to the situation and the sounds they emit are more distinct from each other”, explains Professor Parmentier.

“This difference can certainly be explained by the fact that during the day the fishes use visual (even at a depth of 120 meters) and acoustic cues, they can then use displays to communicate with their own kind. At night, by way of contrast, they are surrounded by absolute darkness which obliges them to ‘refine’ their communication in order to make their own community aware of what they require”.

The results of these ‘auditions’ also makes it possible to open up new channels for studying the impact that anthropic sounds can have on fish communities. “In our recordings, we were clearly able to identify the sounds of engines, boats and other sounds caused by human activity”, explains Eric Parmentier. “We therefore concluded that these sounds could sometimes mask those made by the fish communities studied. The implications of this are such that communications by the fishes can be disturbed by these man-made noises and therefore their way of life is affected too”.  

Read also Nemo really does speaks (ULg-Reflexions 9/5/2007) Ever since Aristotle we know that fish produce sounds. This method of communication relies on several complex mechanisms. Thanks to using original techniques, University of Liège researchers have shown that clownfish produce messages in sound through their oral channels.

(1) Laëtitia Ruppé , Gaël Clément, Anthony Herrel, Laurent Ballesta, Thierry Décamps, Loïc Kéver and Eric Parmentier, Environmental constraints drive the partitioning of the soundscape in fishes, PNAS, April 2015